Process and apparatus for regenerating a photoconductive layer

ABSTRACT

A process for regenerating a photoconductive layer which has been utilized in an electrographic process wherein the layer is regenerated by removing surface particles of the layer from the remainder of the layer. Abrading the layer to remove the surface particles of the layer is the preferred embodiment of performing the process of the present invention. The regeneration can be performed prior to the formation of a latent electrostatic image in an electrophotographic duplicating process. The process of the present invention is especially useful with layers containing organic materials and also when incorporated in an electrophotographic process which includes forming a latent electrostatic image on a surface and transferring the latent electrostatic image from that surface.

United States Patent [191 Lanker Oct. 7, 1975 [75] Inventor: WilliLanker, Zumikon, Switzerland [73] Assignee: Turlabor A.G., Zumikon,

Switzerland 22 Filed: Apr. 29, 1974 21 Appl. No.: 465,248

Related US. Application Data [62] Division of Ser. No. 168,224, Aug. 2,1971, Pat. No.

[52] US. Cl 355/17; 96/1 R; 355/3 R; 355/15 [51] Int. Cl. G03G 13/00[58] Field of Search 355/3 R, l5, 17; 96/1 R; 134/19 [56] ReferencesCited UNITED STATES PATENTS 3,512,966 5/1970 Shattuck et al. 96/1 R3,725,059 4/1973 Komp 355/15 3,770,429 11/1973 Kinoshita et al 355/15 XPrimary Examiner-Richard L. Moses Attorney, Agent, or Firm-Arnstein,Gluck, Weitzenfeld & Minow ABSTRACT A process for regenerating aphotoconductive layer which has been utilized in an electrographicprocess wherein the layer is regenerated by removing surface particlesof the layer from the remainder of the layer. Abrading the layer toremove the surface particles of the layer is the preferred embodiment ofperforming the process of the present invention. The regeneration can beperformed prior to the formation of a latent electrostatic image in anelectrophotographic duplicating process. The process of the presentinvention is especially useful with layers containing organic materialsand also when incorporated in an electrophotographic process whichincludes forming a latent electrostatic image on a surface andtransferring the latent electrostatic image from that surface.

6 Claims, 4 Drawing Figures U.S. Patent Oct. 7,1975 Sheet 2 of43,910,697

U.S. Patent ()ct. 7,1975 Sheet 3 of4 3,910,697

US. Patent 0a. 7,1975 Sheet4 of4 3,910,697

I llllllllllll l I PROCESS AND APPARATUS FOR REGENERATING APHOTOCONDUCTIVE LAYER This is a division of application Ser. No.168,224, filed Aug. 2, 1971, now U.S. Pat. No. 3,815,295.

This invention relates to the treatment of photoconductive layers andmore particularly to regenerating a used photoconductive layer for reusein an electrophotographic duplicating process.

Electrographic processes wherein a chargeable and selectivelydischargeable layer is used and electrophotographic processes utilizingphotoconductive layers which are chargeable and selectivelydischargeable on exposure to a light image are well known to the art. lnone type of process a photoconductive layer is coated on sheets of paperwhich are then used as the image forming surface in the process. Alatent image formed on the surface can be developed to obtain a visiblecopy. In a second type of process, the photoconductive layer is affixedto a cylindrical drum, a plate, or an endless belt and the layer isreused in producing successive copies. It is this second type of processto which the present invention is directed. In the past, thephotoconductive material comprising the photoconductive layer which wasusually affixed to a metal cylinder or plate has been a relatively hard,inorganic material such as selenium or an alloy of selenium and one ormore other metals. More recently organic photoconductive materials,characterized by a softer surface, have been used either alone or incomposition as the photoconductive material in the photoconductivelayers, which are affixed to cylinders, plates, or endless belts.

Commercial photocopying machines utilizing the electrophotographicprocess of the second type described above generally include developinga latent electrostatic image on the surface of the photoconductive layerfollowed by transferring the developed image to a support material suchas a paper sheet. This type of process will herinafter be referred to asthe developed image transfer process. Although in transferring thedeveloped image to the support surface, a large portion of thedeveloper, usually in powder form, is removed from the surface of thephotoconductive layer, residual developer particles remain on thesurface of the layer which must be cleaned to remove the residualdeveloper particles before the photoconductive layer can be reused inproducing subsequent copies. Many methods of removing the residual tonerparticles have been proposed, but even with these methods, the residualdeveloper particles build-up on the surface of the photoconductive layerand are believed to penetrate the surface of the layer, particularlywhere the surface contains imperfections, such as pinholes, scratches,and the like. The preparation of the photoconductive layer for reuseafter such build-up of residual developer particles required specialcleaning steps usually involving temporary removal of thelayer-supporting cylinder or belt from the machine.

The cleaning step required in the developed image transfer processes iseliminated in still another type of process, wherein the latentelectrostatic image is formed and, without development of the latentimage,

the latent image is transferred from the surface of the photoconductivelayer to a support surface. The transferred latent electrostatic imageon the support surface can be subsequently developed on the supportsurface to form the visible image. In this type of process, developerparticles do not contact the photoconductive layer. This latter type ofprocess, which will hereinafter be referred to as the latentelectrostatic image transfer process, is described in several patentsincluding L. E. Walkup, U.S. Pat. No. 2,825,814. Although the necessityof cleaning untransferred developing particles from the surface of thephotoconductive layer has been eliminated by this latter method, lintremoving means can be employed threwith, as disclosed by C. F. Carlsonet al., in U.S. Pat. No. 3,015,304.

While it would be expected that in view of the above advantage, thelatent electrostatic image transfer process would be preferable over thedeveloped image transfer processes, the latent electrostatic imagetransfer process has not as yet been commercially acceptable.

The quality of the copy obtained in repeated use of the photoconductivelayer in both the developed image transfer process and the latentelectrostatic image transfer process deteriorates in proportion to thatuse. However, the deterioration in copy quality upon repeated use isespecially pronounced with layers containing organic materials,particularly layers containing organic photoconductive material. Organicphotoconductive materials, such as polyvinylcarbazole, have theadvantages of low cost and relatively easy production as compared toinorganic photoconductive materials, such as selenium; but thedeterioration as reflected in the deterioration in copy quality, uponrepeated use, is greater with the former than with the latter. Thedeterioration in copy quality can be related to the decrease in thesurface potential, or saturation surface potential, also referred to assurface acceptance voltage or charge acceptance voltage; i.e., themaximum surface potential to which a layer can be charged, and in thedecrease in the dark resistivity of the photoconductive layer uponrepeated use of the layer. As the use of the layer continues, thecontrast of the image, as determined by the difference in potentialbetween the unexposed and exposed areas of the image, decreases untilthe contrast is insufficient to obtain a usable copy. The saturationsurface potential and the contrast potential, as well as the uniformityand constancy thereof, are generally referred to herein as theelectrophotographic properties. Thus, there is a continuing need formethods for regenerating photoconductive layers for reuse inelectrophotographic processes, so as to produce a commerciallyacceptable number of copies from the layer without substantialdeterioration in the quality of such copies.

It is therefore an object of this invention to provide a process whereina photoconductive layer can be regenerated for reuse in anelectrographic process.

Another object of the present invention is to provide for theregeneration of electrophotographic properties of photoconductive layerscomprising material which is susceptible to deterioration of itselectrophotographic properties on repeated use in an electrographicprocess.

Another object of the present invention is to provide a treatment systemwhich improves the electrophotographic properties of a photoconductivelayer which has been utilized in an electrographic process.

Another object of this invention is to provide for the regeneration ofthe electrophotographic properties of photoconductive layers comprisingorganic material which is susceptible to deterioration of itselectrographic properties upon repeated use in an electrophotographicprocess.

Still other objects, features and advantages of the present inventionwill be apparent to those skilled in the art from the followingdescription, appended claims, and annexed drawings.

The above objects and others are accomplished, generally speaking, bytreating a photoconductive layer which has been utilized in anelectrophotographic process, by removing surface particles of thephotoconductive layer from the remainder of the layer. It has now beenfound that the desirable properties of used photoconductive layers,especially organic photoconductive layers, can be restored tocommercially acceptable levels, for example, in the case ofphotoconductive layers containing organic material so as to produce atleast 5,000, preferably above about 10,000, and even more preferablyabove about 20,000 copies of good quality per given area of the layer,by the method of the present invention. Generally, it has now been foundthat the deterioration of the electrophotographic properties of thephotoconductive layer is primarily a surface effect and that thedesirable properties of the photoconductive layer can be regenerated byremoving the particles of the layer which comprise the surface of thelayer. Regeneration by this method is believed to be due to theelimination or substantial reduction of the charge injecting effect thedeteriorated surface particles and moisture have upon the remainder ofthe layer, so as to restore and stabilize the electrophotographicproperties of the layer. The term surface particles as used herein andin the appended claims is intended to mean those particles ofphotoconductive material and other material, if any, which define theexposed surface of the photoconductive layer. The surface particles of aphotoconductive layer which has been used repeatedly in anelectrophotographic process will commonly include decomposed, chemicallychanged layer material and external material from the surroundingatmosphere, such as water. The surface particles may includedecomposition products formed upon reaction of the exposed layermaterial with the surrounding atmosphere.

As a practical matter, it is realized that particles underlying thesurface particles may be removed along with the surface particles.However, removal of such underlying particles, particularly in the caseof organic photoconductive material, organic binder materials, andorganic overcoating layers, have been found to have no substantialdeleterious effect upon the desirable properties of the layer. Theamount of material which can be removed in the regeneration process ofthe present invention is limited by the thickness of the photoconductivelayer. Preferably, as little material as is necessary for regenerationis removed from the layer, but up to about one-tenth to one-third of thethickness of the photoconductive layer or 0.01 to about 1 micron, asmeasured from the exposed surface of the layer toward the oppositesurface of the layer, can be removed in the performance of the processof the present invention. In order to be useful after regeneration, thelayer should have a thickness substantially greater than the thicknessof the material being removed during regeneration. Ph'otoconductivelayers, having a thickness of at least about 3 microns are preferred,and layers having a thickness above about microns are even morepreferred in order to provide sufiicient photoconductive material afterregeneration for the production of copies of good quality.

The process of the present invention can be performed using a number ofsuitable devices. One preferred embodiment of the present inventioncomprises abrading the layer to remove the surface particles. Theabrading can be effected in several ways. One method is to contact thelayer with an abrasive material such as oxides of the various metals,such as zinc, chromium, and aluminum, and some non-metals such assilicon, or the commercially available inert polishing powders.Preferably, the abrasive material has an average diameter less thanabout one micron. Generally, the abrasive material is applied uniformlyacross the layer with a substantially constant pressure in order tosubstantially uniformly remove surface particles from the layer, at asmall rate of abrasion, although uniform removal of the surfaceparticles is not required to effect the regeneration. The rate ofabrasion, as used herein, is the thickness of material removed from thelayer per number of cycles or copies. Removal of the surface particlesis intended to mean separation of the particles from the remainder ofthe layer, and removal of these particles therefrom. Contact of theabrasive material with the layer to obtain the separation and removal ofparticles can be performed by cascading the abrasive materials acrossthe layer, by projecting the material against the layer underpressure,such as air pressure, or by similar contacting methods. The presence ofsmall amounts of inert abrasive material, i.e., material which does notcause deterioration of the electrophotographic properties of the layerupon contact withthe layer, on the surface of the photoconductive layerafter regeneration is not detrimental to the use of the layer in anelectrophotographic reproduction process. Moreover, the presence of suchinert material on the layer may even be an advantage due to a screeningeffect which the abrasive particles have upon the layer. Such advantagecan be noted by a reduction in overdevelopment of edges of images withless development within the edges of the images.

A particularly efficient method of contacting the layer with theabrasive material comprises supporting the abrasive material on a weband contacting, such as by rubbing, the web against the layer. In thismanner, the abrasive material can be applied to the layer homogeneouslyand with a constant pressure, to separate surface particles of the layerfrom the remainder of the layer, and to remove the particles therefromby movement of the web. Abrasive materials which are substantiallyspherical, such as the polishing powders, can be impregnated into theweb, adhesively affixed to the web, or retained thereon by other means.Abrasive materials having diameters in the order of from about 0.1 toabout 1 micron are preferred. Particularly suitable abrasive materialsfor use with webs as described herein are hard, inert inorganicmaterials, such as minerals and oxides, preferably aluminum oxide, zincoxide, titanium dioxide, silicon dioxide or chromium oxide, andmaterials fibrous in shape, such as glass wool or asbestos. The webmaterial may comprise fibrous material, such as animal fur, naturalfibers, such as cotton, wool, hair, cellulose, synthetic furs, paper orcloth.

Still another efficient method of contacting the layer with abrasivematerials is to contact the layer with a web which is itself abrasive.In order to lessen the occurence of deep scratches on the remainingsurface of the layer, it is preferable to utilize abrasive materialshaving small diameters, in the order of about one micron or less, in oron the web. Particularly suitable abrasive materials are those havingthe shape of fibers or needles, which can be incorporated into thesupporting web, such as by being woven therein, or can comprise the webitself. A suitable web of this type is a soft paper web which containsfine glass fibers or other abrasive fibers. These webs can be contactedwith the layer by the use of tensioning rollers or a support surface aswill be hereinafter described. Only slight contact pressures, in theorder of from about to about 100 grams per square centimeter have beenfound to be required when using the web materials described above, andthe pressure may be decreased with increased abrasiveness of the web orthe contact area. The amount of particles and the depth to whichparticles are removed from the layer upon perfonning the regenerationmethod of the present invention using a web as the abrasive surface orsupport can be controlled by adjusting the contact pressure of the webagainst the layer, as described above, by altering the abrasiveness ofthe web, e.g., by changing the nature or properties of the abrasivematerials, or by altering the area of contact, as noted above, as wellas by adjusting the proportion of abrasive mate rial, the speed of theweb relative to the layer, the frequency with which the web is replacedas it becomes less abrasive through use, and the interval and durationof contact of the material with the layer.

A second method of performing the abrading comprises contacting thephotoconductive layer with a rotating brush. The brush preferablycomprises a plurality of bristles affixed to a shaft. The shaft can berotatably mounted adjacent the photoconductive layer with the axis ofrotation either parallel, perpendicular, tangential, or at an angle tothe surface of the layer, and rotated and contacted with the layer asdesired. The bristles of the brush can be formed of any suitablematerial such as the synthetic bristles, and preferably naturalbristles; for example: animal fur, such as rabbit, fox, beaver, hair ofcows ear; goat skin; horse hair; hogs bristles; mixtures thereof; andthe like. The brush used in the method of the present invention forremoval of the surface particles can be very soft, for example, theanimal furs, such rabbit, fox, etc., or goatskin with photoconductivelayers having organic material as their top surface; whereas brusheshaving bristles which have greater coarseness, hardness or stiffnessmust be used with the inorganic layer materials. The bristles preferablyhave a diameter of from about 0.05 to about 0.3 millimeters, and thebrush desirably has a diameter of from about to about 60 centimeters. Itis preferred to contact the brush with the surface of thephotoconductive layer with slight pressure in the order of about 100grams per square centimeter. Excellent result are obtained byperiodically contacting the photoconductive layer with a brush asdescribed above, whose axis of rotation is parallel to the surface ofthe layer, rotating at a speed of from about 1,000 to about 5,000revolutions per minute. Although the brush can be contacted with thelayer after each electrophotographic cycle, it is preferred, especiallyat relative humidities above about 40 per cent, to contact the layerwith the brush less frequently; for example, in the order of once every10, 100, 1000 or 10,000 cycles. Furthermore, it is also preferred toutilize a brush mounted with its axis of rotation at an angle of about45 to about 80 to the surface of the layer so that the bristles contactthe layer at a small angle, for example, from about 10 to about 45. Thelatter embodiment permits the use of brushes of greater stiffness havingadvantage at higher relative humidities, for example, above about 40 percent. In general, short intervals, i.e., small numbers of latent imageforming cycles, between regenerations are preferred, since the surfacepotential decreases with increases in the number of cycles betweenregeneration cycles. In addition, surface particles adhering to thebristles of the brush can be removed therefrom in a manner known to theart for removing particles from brushes, such as by contacting the brushwith a blade or cleaning material, such as polishing paper.

A second embodiment of the method of the present invention forregenerating a photoconductive layer by removing surface particles,comprises washing or wetting the surface of the layer with a solvent. Inone form the solvent may be applied to the layer by moving the layerthrough a body of the solvent or by flowing the solvent over the layer.In another method of applying the solvent to the layer, a fibrous webcan be wetted with the solvent and the web then contacted with the layerin a manner similar to the application of a web supporting or containingan abrasive material to the layer. Washing the layer can also beadvantageous when combined with another regeneration method, such asheretofore described, to further assist in removing, as by washing,separated particles and/or abrasive material from the surface of thelayer. The photoconductive layer preferably is removed from contact withthe solvent or other liquids when the layer is not being utilized forits intended function, as when electrophotographic copying using thelayer has ceased.

Still another embodiment of this invention comprises the removal ofsurface particles using thermal means, such as radiation or heat. Theperformance of this embodiment can be accomplished by applying infraredradiation to the layer or by other means as hereinafter described.

The method and apparatus of the present invention will become evenfurther apparent from the following description of the invention andfrom the drawings wherein: I

FIG. 1 is a schematic illustration of means for regenerating aphotoconductive layer according to one embodiment of this invention.

FIG. 2 is a schematic illustration of means for regenerating aphotoconductive layer according to another embodiment of this invention.

FIG. 3 is also a schematic illustration of apparatus for regenerating aphotoconductive layer according to still another embodiment of thisinvention.

FIG. 4 is a schematic illustration of a modification of the embodimentof the present invention schematically illustrated in FIG. 1.

Referring now to FIG. 1, there is shown a cylindrical drum 10 having anouter photoconductive layer 12 of photoconductive insulating materialsupported by a conductive inner surface 14 which may be of metal. Thephotoconductive layer may contain any suitable photoconductive materialsuch as selenium, cadmium sulfide, or any of the organic photoconductorsknown to the art, such as polyvinylcarbazole, or any of the copolymersor derivatives thereof. The photoconductive layer may consist only ofthe photoconductive material or may contain organic material, forexample, a binder material such as an organic resin, or a top surfacematerial, preferably of organic material, and preferably the top surfacematerial is at the surface of the photoconductive layer, or othermaterials, and may contain one or more sensitizing dyes. For thepurposeof this invention, the top surface layer in oron photoconductive layer12 may be treated in the same manner as the photoconductive layer. I

In an electrophotographic process, a latent electro static image isformed on the surface of the photoconductive layer 12 by means ofapplying a uniform charge to the photoconductive layer 12 and exposingthe charged layer to a light pattern to selectively dissipate the chargeon the layer 12 in accordance with the light pattern.

'The uniform charge can be applied to the layer 12 by use of a chargingdevice, such as corona unit 16. Typically, corona unit 16 includes oneor more thin charging wires 18 surrounded by a conductive shield 20. Apower supply such as DC. source 22 is connected to the charging wires'18 and is also connected to the conductive inner surface 14 supportingthe outer layer 12 of photoconductive insulating material by known meanssuch as a direct connection (not shown) or through ground. Theconnection between the conductive inner surface 14 and the power source22 is completed in the embodiment of FIG. 1 by means of a contact 24electrically connected to shaft 26 of drum The step of exposing thephotoconductive layer 12 bearing a uniform charge on its surface to alight pattern is performed by means of an illumination and projectionsystem 28 comprising at least one illumination source 30 mounted in asuitable reflector 32 and a lens 34. To effect the exposure step, anoriginal document 36 to be copied is transported by means (not shown)known to the art through the exposure station wherein light from theillumination source 30 and/or light reflected from the reflector 32illuminates the surface of document 36 to be copied and the light raysare reflected through lens 34 onto the surface of photoconductive layer12. The light rays from illumination source 30 and/or reflector 32 arereflected from the document 36 in varying intensity according to theabsorption of the rays by the surface of document 36 bearing a visibleimage. The resultant reflected rays form a light pattern correspondingto the visible image on the document 36. The rays comprising the lightpattern are projected by lens 34 onto the surface of the photoconductivelayer 12 where they selectively discharge the uniform charge on thesurface of photoconductive layer 12 in accordance with the intensity ofthe reflected rays. Thus, rays of relatively high intensity beingreflected from white or light, usually background, areas of the visibleimage on document 36 cause the discharge of the uniform charge on thephotoconductive layer 12; whereas rays of low intensity reflected fromdarker areas of the document or the absence of rays due to totalabsorption of the illuminated rays from source 30 and/or reflector 32,do not discharge the uniform charge or discharge the uniform charge onphotoconductive layer 12 to a lesser extent in accordance with thephotoconductive. properties of the layer. In this manner, the uniformcharge applied to the photoconductive layer 12 by corona unit 16 isselectively discharged or dissipated to form a latent electrostaticimage on the surface of the photoconductive layer 12.

. The latent electrostatic image on the surface of photoconductive layer12 can be utilized in several manner's known to the art. As heretofordescribed, the latent electrostatic image on the surface ofphotoconductive layer 12 can be developed by various means known to theart and the developed image transferred to a receiving sheet or othersuitable surface. The transferred developed image can then be fixed onthe receiving surface by suitable means such as the application ofinfrared rays. The surface of photoconductive layer 12 after thetransfer step can then be cleaned as known to the a t, and reused in thenext cycle of the apparatus. Cleaning of excess or residual developerremaining on the surface of the photoconductive layer after transfer ofthe developed image is distinct and dissimilar from the process of thepresent invention, as in the cleaning step the surface of the layer ismerely wiped or lightly brushed to wipe or brush away the surplusdeveloper, but care is taken not to abrade or scratch the surface of thelayer; whereas in the process of the present invention the surfaceparticles of the layer must be removed, for example by abrading, toeffect regeneration of the electrophotographic properties of the layer12. In the developed image transfer processes, such as the processdescribed above, the process of the present invention extends the usablelike of the photoconductive layer by regenerating the photoconductiveproperties of the photoconductive layer.

However, the process of the present invention is especially useful inthe latent electrostatic image transfer process, such as the processutilized by the apparatus shown in FIG. 1. In this apparatus, the latentelectrostatic image on the surface of photoconductive layer 12 istransferred by means of transfer apparatus 38 to a transfer sheet, suchas sheet 40, which may be a sheet having a dielectric coating. Sheet 40is fed from a stack of sheets 42 by a feed roller 44 into a sheetfeeding path 46 consisting of guiding members 48 and rollers 50. Thesheet 40 is advanced along sheet feeding path 46 onto a conveyor 52which is normally in contact with the surface of the photoconductivelayer 12, or slightly spaced therefrom. Conveyor 52 consists of one ormore endless belts of material such as mylar or rubber having aresistance greater than that of the photoconductive layer 12. As thesheet 40 is conveyed into contact with the photoconductive layer 12, thelatent electrostatic image on the photoconductive layer 12 istransferred to the sheet 40 by means known to the art and preferably bythe application of a field.

In the apparatus shown in FIG. 1, the field is applied by means of atransfer corona unit 56 consisting of at least one corona discharge wire58 partially surrounded by a conductive shield 60. A potential isapplied to corona discharge wire 58 by means of a source of potential 62which in turn is also connected to the conductive inner surface 14 ofdrum 10 by direct connection (not shown) or through ground and contact24 and shaft 26. The potential required for transfer of the latentelectrostatic image is known to the art from various patents, such asUS. Pat. No. 2,825,814 heretofore described.

Following transfer, in the apparatus shown in FIG. 1, the receiver sheet40 is conveyed by conveyor 52 along a second path 64 to a developingstation 66. The developing station 66 shown in FIG. 1 comprises a tankor tray 68 containing a liquid developer 70 as known to the art, such asliquid toner disclosed in Wagner US. Pat. No. 3,438,904. The liquiddeveloper 70 is applied to the receiver sheet 40 by immersing the sheetin liquid developer 70 by guiding the sheet along a partially submergedguiding member 72. Sheet 40 is removed from developing station 66 by theleading edge of the sheet contacting a pair of rollers 74 which advancesthe sheet along second path 64. Sheet 40 next reaches drying station 76wherein the developed image on the sheet is fixed to the sheet byevaporating liquid components of liquid developer 70 and preferably byheating and fusing developer from liquid developer on and in the surfaceof the sheet. The drying station 76 can consist of infrared sources 78mounted in a reflecting shield 80. Sheet 40 is next exited from secondpath 64 into a receiving tray 82.

Any charges remaining on photoconductive layer 12 are discharged bymeans of a light source 84 mounted adjacent the surface ofphotoconductive layer 12 in a reflecting light shield 86 subsequentalong the direction of rotation of drum to the developing station 56.Naturally, to effect the discharge of the remaining charges, thespectrum of light source 84 desirably corresponds to the spectrum of thephotoconductive material in photoconductive layer 12.

Referring further to FIG. 1, the apparatus of the present invention isshown therein as a brush 87 mounted to be contactable with the surfaceof photoconductive layer 12. Brush 87 comprises a plurality of bristles88 mounted on a shaft 89. The brush 87 can be permanently mounted incontact with photoconductive layer 12, thus effecting regeneration ofthe photoconductive layer 12 upon each cycle of the layer 12 through thevarious steps within the electrophotographic process, or, as shown, canbe spaced apart from contact with the photoconductive layer 12, butmounted so as to be selectively contactable with the layer. For example,brush 87 can be mounted on a member 90 pivoted by a shaft 92 by asolenoid plunger 94. Thus, when switch 95 is closed, an electricalcircuit is completed connecting electrical source 96 to solenoid coil 98causing solenoid plunger 94 to force member 90 to pivot about shaft 92so that brush 87 is placed into contact with the surface ofphotoconductive layer 12. Upon opening switch 95, the connection ofsource 96 to solenoid coil 98 is broken, releasing solenoid plunger 94from member 90. Brush 87 is withdrawn from contact with photoconductivelayer 12 by means of spring 100 affixed to member 90 and on the otherside to frame 102 of the apparatus, causing brush 87 to be withdrawnfrom contact with the photoconductive layer 12. In this manner, switch95 can be periodically closed to cause brush 87 to be periodicallycontacted with the surface of photoconductive layer 12 for regeneratingthe photoconductive properties of the layer. Switch 87 can be replacedby suitable automatic means, such as an automatic counter, so as tocomplete the circuit periodically, for example after a predeterminednumber of cycles, e.g. revolutions of drum 10, or after a predeterminednumber of receiving sheets have been processed through the apparatus.

In FIG. 2, another embodiment of apparatus according to the presentinvention is illustrated, wherein elements similar to elements in FIG. 1have the same reference numerals. In this embodiment, the cylindricaldrum 10 provided with an outer photoconductive layer 12 is constructedand arranged in the same manner as in the case of the embodiment shownin FIG. 1. The charging unit 16 and the illumination and projectionsystem 28 as well as the light source 84 and reflector 86 fordischarging residual charges on the surface of photoconductive layer 12correspond with the appropriate apparatus of FIG. 1 and are referencedin the same manner so that a repeated description is unnecessary.

Referring to FIGS. 1 and 2, in place of the conveyor 52 of transferstation 38, according to FIG. 2 a web of receiving material is suppliedfrom a roll of Web material 122 and is applied in intimate contact withthe photoconductive layer 12 by means of rollers 124 and 126. Suitabletensioning apparatus (not shown) can be included to maintain contact ofthe web 120 against the photoconductive layer 12. The latentelectrostatic image on the surface of photoconductive layer 12 formed bymeans of the corona unit 16 and the illumination and projection system28 is transferred from the surface of the photoconductive layer 12 tothe receiving web 120 by the application of a field by means of coronadischarge unit 128. Discharge unit 128 comprises at least one coronadischarge wire 130 partially surrounded by a conductive shield 132. Thecorona discharge is effected by connecting a source of potential 134 tocorona discharge wire 130 with the other terminal of source 134 beingconnected to the conductive inner surface 14 of drum 10 either by directconnection (not shown) or through ground and contact 24 and shaft 26.After the web 120 receives the transferred latent electrostatic image,it is advanced to a developing station 136 comprising, in thisembodiment, a tank 138 containing solid, powdered toner 140 which isknown for use in developing latent electrostatic images. The powderedtoner 140 is applied to the surface of web bearing the transferredlatent electrostatic image by means of a magnetic brush 142 comprisingmagnets mounted about a common axis and particles of material attractedby the magnet which carry the toner particles by magnetic attractionfrom the tank 138 to the said surface of web 120. Magnetic brushes ofvarious types are known and can be utilized in this embodiment of thepresent invention. Subsequent to passage through developing station 136,the web is advanced past a fixing station 144 generally similar todrying station 76 of FIG. 1. Fixing station 144 comprises one or moreinfrared heating elements 146 partially surrounded by a reflectiveshield 148. In this manner, the visible image on the web 120 resultingfrom the development of the transferred latent electrostatic image atdeveloping station 136 is fused and bonded to the surface of thereceiving web 120. Thereafter, the receiving web 120 is collected on atake-up roll 150. Web 120 may be advanced by driving take-up roll 150synchronously with the rotation of drum 10.

Following the transfer of the latent electrostatic image from thesurface of photoconductive layer 12 to the surface of receiving web 120,the photoconductive layer 12 is rotated on drum 10 past illuminationsource and reflector and light shield 86 to discharge any chargesremaining on the surface of photoconductive layer 12 to washing station152. Washing station 152 represents, schematically, the embodiment ofthe present invention wherein photoconductive layer 12 is regenerated byremoving surface particles of the layer by washing the layer with asolvent, i.e., a liquid which is a solvent for the surface particles,preferably selectively a solvent for decomposed material, moisture, andother contaminants, but not substantially for undeteriorated material inthe layer. Thus, as shown in FIG. 2, photoconductive layer 12 is rotatedthrough a body of a liquid 154, which can be a solvent, for theparticles comprising the surface of photoconductive layer 12. Forexample, where the photoconductive layer consists of polyvinylcarbazole,ethanol has been found to be a suitable solvent for surface particlesthereof.

The liquid 154 preferably is a poor solvent for undeteriorated materialin the photoconductive layer 12. The washing action can be effectivelyattained by combining the washing with another method for removingsurface particles of the layer, such as those described herein. Forexample, as shown in FIG. 2, the washing station further preferablyincludes a body of solid material 156 which contacts the surface oflayer 12 and the liquid 154. Solid material 156 may be in the form of asponge or folded or thick cloth (not shown) and preferably may beabrasive to layer 12 so as to remove surface particles from layer 12 byabrading the layer in the presence of liquid 154. In this manner theliquid 154 may be a very poor solvent for layer 12, but will assist theremoval of surface particles, as by washing separated particles from thesurface of layer 12. By rotation of drum l and thereby rotation of thephotoconductivec layer 12 through the washing station 152, thephotoconductive layer 12 is contacted with both the solid material 156and the liquid 154 to remove, by abrading and washing and/or bydissolving, the surface particles from the layer. Other surface particleremoving means, such as a web of paper or cloth or a brush, may besubstituted for the solid material 156 to effect the abrading andwashing operations.

A further embodiment of apparatus according to the present invention isillustrated in FIG. 3, wherein elements similar to elements in FIGS. 1and 2 likewise have the same reference numerals. In this embodiment,

- the washing station 152 of FIG. 2 is replaced with a web contactingstation 160. Web contacting station 160 comprises a web 162 and roller164 which maintains contact of the web with the surface ofphotoconductive layer 12. Web 162 is supplied from supply roll 166, isadvanced by the roller 164 toward and away from the surface ofphotoconductive layer 12, and is gathered by suitable means (not shown)onto a take-up roll 168. By the use of the apparatus shown in FIG. 3, alatent electrostatic image is formed on the surface of photoconductivelayer 12 by first applying a uniform charge to the layer by use ofcorona unit 16 and by selectively discharging the uniform charge on thesurface of photoconductive layer 12 by means of illumination andprojection system 28. The latent electrostatic image is next transferredto a receiving web 120 by means of transfer corona unit 128. Residualcharges on the surface of photoconductive layer 12 are discharged byillumination source 84 and reflector light shield 86. Surface particlesof the photoconductive layer 12 are removed therefrom by means of webcontact station 160 to regenerate the photoconductive layer 12 for usein the next cycle of the apparatus in accordance with this invention.

As heretofore stated, the web 162 desirably supports abrasive materialon its surface and is contacted with the surface of photoconductivelayer 12 by means of roller 164 providing support to the back of web162,

and maintaining the web against the layer 12, thereby abradingphotoconductive layer 12 to remove the surface particles therefrom.Gentle abrading action can be obtained by advancing the web 162 in thedirection of, and at the peripheral speed of the rotation ofphotoconductive layer 12. Increased abrasive action can be obtained byadvancing web 162 in the same direction as the direction of rotation ofphotoconductive layer 12 at a speed substantially greater than theperipheral speed of photoconductive layer 12, or by advancing the web inthe same direction as the direction of rotation of photoconductive layer12, but at a speed less than the peripheral speed of the photoconductivelayer. Further increased abrasive action can be obtained by advancingthe web at reduced speeds, by stopping the web during the regenerationstep, or by advancing the web in a direction opposite to the directionof rotation of photoconductive layer 12. The amount of abrasion can alsobe controlled by adjusting the pressure that the roller 164 exerts onthe back of web 162 to provide increased or decreased pressure of theweb 162 against the photoconductive layer 12. Thus, the severity ofabrasion can readily be controlled in accordance with the amount ofmaterial, i.e., surface particles and particles thereunder to beremoved, and in accordance with the abrasiveness of the material on thesurface of web 162.

As heretofore stated, web 162 can desirably be a web which is itselfabrasive. A very suitable web 162 was prepared of paper containing fineglass fibers as the abrasive. The preparation of the web will behereinafter described.

In FIG. 4, a modification of the apparatus illustrated in FIG. 1 isschematically illustrated, wherein elements similar to elements in FIG.1 have the same reference numerals. The function of these similarelements and the formation and transfer of the image have been describedheretofore.

As illustrated in FIG. 4, following the transfer of the latentelectrostatic image from the surface of photoconductive layer 12 to thesurface of sheet 40, the photoconductive layer 12 is rotated on v drum10 past illumination source 84 and reflector and light shield 86, todischarge any charges remaining on the surface of layer 12, to brushingunit 170. Brushing unit can comprise a generally circular brush 172formed of bristles affixed to a shaft 174, which rotatably supportsbrush 172 at an angle to the surface of photoconductive layer 12.Preferably, the brush is supported at a large angle, for example, fromabout 45 to about 80 degrees to the surface of the photoconductive layer12 if flat, or to the tangent at the point of contact if the surface ofthe layer 12 is curvilinear as in FIG. 4. In this preferred manner thebristles forming the brush will contact the layer 12 at a smaller angle,for example from about l0 to about 45, Shaft 174 supporting brush 172can be rotated by suitable means, such as a motor 176 which in turn maybe guidingly supported upon a guiding member 178, which advantageouslymay be a rack, by a bracket 180 which may include a pinion. Preferably,brush 172 is moved parallel to the axis of shaft 26 of drum 10 and hencethe surface of layer 12 by known means (not shown) during operation sothat the entire surface of photoconductive layer 12 is uniformlycontacted with the brush during the process of the present invention.Movement in this manner can be accomplished by reciprocally moving motor176 which supports shaft 174 and brush 172 along guiding member 178which can be mounted parallel to the axis of shaft 26.

Brush 172 may be rotated at any desired speed, and preferably the brushis rotated rapidly, for example at speeds in the order of 10,000 to20,000 revolutions per minute. Similarly, the pressure at which thebrush contacts layer 12 can be varied, but small pressures, in the orderof 50 to 100 grams over a small area such as 0.2 square millimeters, arepreferred. The brush desirably has a diameter of from 10 to 20millimeters comprising bristles having a diameter of from 0.1 to'O.2millimeters, although harder or softer brushes can be used. As in thecase of the embodiment illustrated in FIG. 1, the regeneration step maybe performed at every cycle of the drum 10, or preferably periodicallyat intervals, such as at every 10, 100, 1,000, 10,000 imaging cycles ofthe drum.

The present invention is further described and specifically defined inthe following examples. The examples are intended to illustrate thevarious preferred embodiments for carrying out the invention.

EXAMPLE 1 A comparative test was conducted with apparatus similar to theapparatus illustrated in FIG. 1. In this test, Photoconductive LuvicanM- l 70 obtained from Badische Anilin-Soda Fabrik, Germany,polyvinylcarbazole, mixed with 3 percent tetranitrofluorenone and 20percent plasticizer, Dowtherm A obtained from Fluka A.G., Buchs,Switzerland, was coated to a thickness of from 5 to 6 microns onaluminum foil. The

coated foil was taped onto an aluminum drum so that the underside of thefoil was in electrical contact with the drum. Upon rotation of the drumin the dark, the coated foil was charged using a corona unit having anapplied voltage of minus 10 kilovolts, direct current. At the exposurestation, the coated foil was exposed to image-wise incandescent light atan exposure of 1 l4 luxseconds. The latent electrostatic image formedwas transferred after a predetermined number n of charging anddischarging cycles of the drum. In the cycling without transfer of thelatent electrostatic image, the latent electrostatic images weredischarged with a incandescent discharge lamp prior to formation of thesubsequent image. In the cycling with transfer, transfer of the latentelectrostatic image to a sheet of dielectric paper supported on a metaldrum across an air-gap of about 60 microns was effected with the use ofatransfer voltage of about 130 volts D.C. applied across the drumssupporting the respective surfaces. The drum supporting thephotoconductive survace was revolved at a speed of 20 revolutions perminute and the second I drum also revolved at the same speed. Therelative humidity during the test was approximately 50 percent. Duringthe cycles in which transfer of the latent electrostatic image waseffected, the transferred latent image was developed with liquid toner,commercially available from SCM Corporation, New York, USA. The uniformcharge on the surface of the photoconductor was measured at a point fromabout 1 to about 2 inches subsequent to the charging station.Regeneration of the photoconductive layer was effected by brushing thesurface of the layer with a commercial bottle cleaning brush, i.e.,synthetic plastic bristles having a diameter of 0.1 millimeter, thebrush having a diameter of about millimeters, revolving at 2,000revolutions per minute. to remove the surface particles of Cycle No.

No. of the Cycles Including the Regeneration Step Surface Voltage, as aPercentage of the Surface Voltage at the First Cycle 0 100 10,000 0 010,200 200 18,000 8,000 55-60 24,000 14,000 approx. 50

Comparison of identically developed latent electrostatic images on thedielectric paper before and after the cycles which included theregeneration step, showed an improvement of the copy quality after thesaid cycles. Specifically, large white spots on the otherwise darkareas, corresponding to the dark areas in the original, were present inthe sheets made prior to the cycles containing the regeneration step,whereas such areas were not present in the dark areas in the sheetsobtained after the said cycles. In addition, test areas of sheetsobtained after the said cycles had greater contrast as compared to thebackground thereof, as compared to the sheets obtained prior to the saidcycles.

EXAMPLE 2 Example 1 was repeated except that a brush of goatskin havinga diameter of about 60 millimeters rotating at about 1,200 revolutionsper minute was utilized at percent relative humidity in place of thesynthetic bristle brush. Copies of relatively good quality were obtainedafter 2,000 imagingcycles where the brush was contacted with the drum ateach cycle, as compared to copies obtained without the application ofthe brush.

Similarly, the regeneration effect was obtained by the application ofother brushes of goatskin, horse hair, and synthetic bristles rotatingat from 1,000 to 5,000 revolutions per minute at cycling intervals offrom every imaging cycle to once every 1,000 imaging cycles with thephotoconductive layer described in Example I.

EXAMPLE 3 Apparatus similar to that illustrated in FIG. 3 including ametal drum coated with the photoconductive layer defined in Example 1was utilized in this example. Paper webs were prepared by disintegratingtissue paper, Linsoft, obtained commercially from Migros Co.,Switzerland, into water by soaking the paper therein and adding glasswool having a fiber diameter of about 5 to 20 microns in predeterminedamounts. The suspension was mixed and dried. Upon drying, soft paperwebsof about micron thickness containing predetermined amounts of glass woolwere obtained.

The drum described above supporting the photoconductive layer wasrotated with a web prepared as above containing 20% by weight glass wooland having a relatively rough surface pressed against the layer bya-roller having about millimeters of soft sponge rubber as its surfacewith a pressure of 50 grams per square centimeter, over a contact areaas wide as the photoconductive layer and having a length of 2centimeters. By measurement, it was found that the use of the percentglass wool web at the above described conditions of contact resulted inan abrasion rate of one micron per 1,000 cycles. The abrasion rate wasfound to increase about linearly from 2 to about 40 percent glass woolwith increased proportions of glass wool in the web, and conversely theabrasion rate decreased as the proportion of glass wool in thewebdecreased. Similarly the abrasion rate increased with increasingpressure applied to the web against the drum and decreased withdecreasing pressure. The electrophotographic properties of the layer, asevidenced by the saturation surface voltage, were regenerated tocommercially acceptable levels in this example even at high relativehumidity. For example, after 1,000 cycles at 70 percent relativehumidity, with the paper web contacting the layer at every cycle, thesaturation surface voltage measured as in EXample 1', was 70 percent ofthe voltage measured at the first cycle; whereas without the use of thepaper web, the voltage measured zero percent of the voltage at the firstcycle. Copies produced using latent electrostatic image transferapparatus, similar to that described in Example 1, to transfer the imageto a dielectric coated sheet and develop the latent image, after 1000imaging cycles of the layer at 70 percent relative humidity with thepaper web contacting the layer at each cycle, were of good copy quality;whereassheets obtained from the identical number of cycles under thesame conditions, but

without contact of the web with the layer, did not have any visibleimage on the sheet after development.

EXAMPLE 4 The abrasion rate of one micron per 1000 cycles obtained inExample 3 was found to be a limiting factor if regeneration of thephotoconductive layer is to take place at each photocopy cycle or atsome small number of photocopy cycles. Therefore, an abrasion rate offrom about 0.01 to about 0.1 micron per 1,000 cycles is obtained bypreparing, in the manner described above, paper webs having a thicknessof about 50 to about 100 microns (about 15-30 grams per square meter)containing from about '1 to. about 10 percent, and preferably 5 percent,glass wool having a fiber diameter of less than 5 microns preferablyless than about '2 microns. These webs are contacted with the surface ofthe photoconductive layer at a pressure of from about 10 to about 30grams per square centimeter to obtain the desired abrasion rate uponcontinuous contact. Regeneration of the photoconductive layer upon usein an electrophotographic process accomplished by applying the web tothe surface of the layer periodically, for example, once every 10 to 100cycles of the electrophotographic process, also reduces the abrasionrate. In this manner, the photoconductive layer can be utilized in from10,000 to 100,000 electrophotographic cycles per 1 micron in thicknessof the photoconductive layer until the layer becomes too thin to providean electrostatic image which is acceptable upon development andpreferably upon transfer and development. In addition, the paper web canbe advanced past the area of contact with the photoconductive layer at aspeed in the order of 0.1 to 1 meter per 1,000 regeneration cycles.

EXAMPLE 5 A web of tissue paper, prepared from Linsoft, obtained fromthe Migros Co.,.Switzerland, whose surface was covered withapproximately 0. l0.2 milligrams per square centimeter of aluminum oxidepowder, having a diameter of approcimately 0.05 micron was used in thisexample with apparatus similar to that illustrated in FIG. 3. Uponcontact of the powder covered paper web to the surface of thephotoconductive layer, controlled removal of surface particles of thephotoconductive layer was obtained. The contact of the web to the layerwas made with a presence of approximately 50-100 grams per squarecentimeter applied to the web. After 1,200 imaging cycles at 60 percentrelative humidity, which included imaging cycles wherein the web wasapplied to the layer as described above, the saturation surface voltagemeasured as described in Example 1, was 60 percent of the voltage at thefirst cycle. Where the web was not used, i.e., no regeneration stepafter 1,200 imaging cycles, the voltage measured was 20 percent of thevoltage at the first cycle.

EXAMPLE 6 Example 5 was repeated using paper webs as described inExample 4, covered with similar amounts of polycrystalline zinc oxide.These webs, when applied to the surface of the photoconductive drumunder the same conditions of applied pressure and relative humidity,abraded the surface of the photoconductive layer to remove surfaceparticles and thereby provide regeneration of the photoconductive layer.For example, after 10,000 imaging cycles including 200 cycles where theweb was applied, the saturation surface voltage, measured as in Example1, was 50 percent of the voltage at the'first cycle. Where the web wasnot utilized, after 10,000 imaging cycles the voltage was zero percentof the voltage at the first cycle.

EXAMPLE 7 The photoconductive layer described in Example 1 was placed ona metal drum in the manner described therein surrounded with thecharging, voltage measuring, imaging and discharging apparatus describedin that example. The brush apparatus in Example 1 was replaced with atubular infrared lamp of about watts mounted in a cylindrical mirroredreflector mounted adjacent the surface of the photoconductive layer soas to heat the said surface to a temperature of from about 120 to aboutCentigrade. After 10,000 imaging cycles at a relative humidity of 50percent with the infrared lamp heating the layer at each cycle, thesaturation surface voltage was measured as in Example 1 and found to be70 percent of the voltage at the first cycle. However, after 10,000imaging cycles under the same conditions without the use of the infraredlamp, the saturation surface voltage was zero percent of the voltage atthe first cycle.

EXAMPLE 8 A photoconductive layer on a metal drum as described in theprevious example was similarly surrounded with the charging, measuring,imaging and discharging apparatus described in Example 1. Theregeneration step of the present invention, when used, was effected bycontacting the layer lightly with facial tissue paper, Linsoftcommercially obtained from the Migros Co., Switzerland, wetted withethanol. After 10,000 imaging cycles at 50 percent relative humidity,with the application of the ethanol-wetted tissue paper for 100 cycles,the saturation surface voltage was 50 percent of the voltage at thefirst cycle; whereas after the same number of imaging cycles without theuse of the wetted tissue, the saturation surface voltage was Zeropercent of the voltage at the first cycle.

EXAMPLE 9 Apparatus similar to the apparatus described in FIG. 4 wasutilized in this example. Various photoconductive layers were coated onaluminum foil and the foil affixed to a metal drum. The charging,voltage measuring, imaging and discharging apparatus described in theprevious examples was utilized with the drum under the conditionshereinafter described. The regeneration step was performed using thefollowing motor driven brush: Moto-tool, model no. 2, kit 1, brush no.A-3, obtained from Dremel Manufacturing Co., Wisconsin, U.S.A., thebrush having a diameter of 18 millimeters and a bristle thickness of 0.2millimeters, mounted as shown in FIG. 4, with the bristles being at anangle of between about 30 and about 40 to the tangent of the layer atthe point of contact, The apparatus applied the bristles of the brush tothe layer with a pressure of approximately 80 grams over the limitedarea of contact while at rest. In operation, the brush was rotated atabout 10,000 to about 20,000 revolutions per minute for about 0.01 toabout 0.02 second at each portion of the layer per cycle of the drum.

Using the photoconductive layer described in Example 1, after 6,000imaging cycles at 70 percent relative humidity, without the applicationof the brush the saturation surface voltage was 2 percent of the voltageat the first cycle. After one additional cycle with the application ofthe brush as described above, the saturation surface voltage was 70percent of the voltage at the first cycle. Copies were obtained inanother identical experiment using the latent electrostatic imagetransfer apparatus and procedure described in Example 1. Without the useof the brush, copies having very poor copy quality were obtained after500 imaging cycles; whereas where the brush was applied as describedabove at each 100th cycle, copies having good copy quality were obtainedafter more than 3000 imaging cycles. In similar experiments utilizingthe same photoconductive layer, at thicknesses varying from 3 to 20microns, under conditions of from 30 to 80 percent relative humidity,distinct increases in the saturation surface voltage were obtained afterfrom 1,000 to 40,000 imaging cycles by the use of the brush describedabove as compared to operation without the use of the brush.

Similarly, using the photoconductive layer described in Example 1 at aninitial thickness of microns in the apparatus described above, at 40percent relative humidity the saturation surface voltage was measured atevery 6000 imaging cycles up to a total of 36,000 cycles. Before theapplication of the brush described above at each 6000th cycle, thesaturation surface voltage was from 40 to 50 percent of the voltage atthe first cycle; while after the application of the brush at each 6000thcycle, the saturation surface voltage was from 65 to 80 percent of thevoltage at the first cycle. At the 36,000th cycle, copies were obtainedof the image using the latent electrostatic image transfer apparatus andprocedure described in Example 1 immediately before and afterregeneration of the properties of the layer by the application of thebrush. The copier obtained after the regeneration step were found tohave increased contrast and resolution with less defects including spotsand developed background, as compared to the copies obtained before theregeneration step.

Other photoconductive layers without sensitizers or with othersensitizers, such as trinitrofluorenone ortrinitrofluorenonemalonitrile, and without plasticizers, or with otherplasticizers, such as Arochlor 1221, obtained from Monsanto Co., U.S.A.,as well as other photoconductors, for example, brominatedpolyvinylcarbazole, provided similar regeneration of theelectrophotographic properties of the layer upon application of thebrush described above.

It has been found that humidity has a strong influence on theoperational lifetime of photoconductive layers and in particular, ororganic electrophotographic layers. It has been further found that theinfluence of hu-' midity is related and appears to accelerate thedeterioration in the quality of copies as heretofore described, uponrepeated use of the photoconductive layer in an electrophotographicprocess which includes charging the layer with corona discharge meansand/or transferring an image therefrom utilizing corona discharge meansor an electric field. The deterioration effect, i.e., the decrease ofthe charge acceptance of the layer and, hence, the contrast voltage ofthe latent electrostatic image, with increasing humidity, was found,particularly with organic photoconductors, such as polyvinylcarbazole,to depend primarily upon the relative humidity and only slightly, if atall, upon the absolute humidity.

The method of the present invention, particularly using soft brushes,often at every operation cycle, has been found to be effective inregenerating the electrophotographic properties of the photoconductivelayer to a considerable extent at low relative humidities, e.g. belowabout 40 percent relative humidity, and to a somewhat lesser extent athigher relative humidities. Good regeneration can be obtained accordingto this invention at higher relative humidities, such as at 50 topercent or higher relative humidity, by using relatively hard brushes,e.g. the brush of Example 9 periodically at every 10th, th or l000thcycle, or by using abrasive webs, such as that described in Example 3 atevery cycle or at every 10th, 100th or l0OOth cycle.

It has now been found that by heating the surface of the photoconductivelayer, the effect of humidity is diminished. Therefore, it isadvantageous to apply heat to the photoconductive layer prior to, duringand/or subsequent to the regeneration method of the present invention inthe presence of relative humidity above about 40 percent relativehumidity to achieve the desirable regeneration of the present invention.For example, while Example 7 and 8 show excellent regeneration effectsat 50 percent relative humidity, the effects almost disappeared duringoperation at 70 percent relative humidity. However, the application ofheat to the photoconductive layer permits the regeneration effects evenat high humidities, as illustrated in the following example.

EXAMPLE 10 Example 2 was repeated without producing copies with theaddition of a l 10 volt, watt infrared lamp supplied with 60 volts ofpotential placed adjacent the drum and partially surrounded by acylindrical mirrored reflector so as to heat the surface of thephotoconductive layer to a temperature in the order of about 100 C atthe area of contact of the layer by the rotating brush. Upon utilizingthe heating effect of the infrared lamp during the contacting of therotating brush with the surface of the photoconductive layer, at 70percent relative humidity, the smearing on the surface of the layer ofsurface particles separatedted from the layer, as occurs withoutheating, was greatly reduced.

In addition, the application of heat alone has the beneficial effect ofat least partially regenerating the desirable properties of thephotoconductive layer by removing surface particles therefrom byevaporation, as illustrated in Example 7 herein, as well as to decreasethe relative humidity of the atmosphere adjacent the layer to permit theother embodiments of the present invention to regenerate the desirableproperties of the photoconductive layer to a greater extent at thehigher relative humidity.

While only a limited number of embodiments have been illustrated anddescribed, it will be apparent to those skilled in the art that variousmodifications and improvements may be made without departing from thescope and spirit of the invention. Accordingly, it is to be understoodthat the invention is not to be limited by the illustrative embodiments,but only by the scope of the appended claims.

I claim:

1. A process for regenerating a photoconductive layer having asubstantial amount of an organic material which has been utilized in anelectrophotographic process comprising removing surface particles of thephotoconductive layer from the remainder of the layer by applyingthermal radiation to the surface of said layer for removal of saidparticles of decomposed material by vaporization.

2. A process for regenerating a photoconductive layer having asubstantial amount of an organic material which has been utilized in anelectrophotographic process comprising removing surface particles of thephotoconductive layer from the remainder of the layer, wherein theremoving includes washing said layer with a solvent to remove surfaceparticles of decomposed material from said layer.

3. A process for regenerating a photoconductive layer having asubstantial amount of an organic material which has been utilized in anelectrophotographic process comprising removing surface particles of thephotoconductive layer from the remainder of the layer, wherein saidremoving includes contacting said layer with a fibrous web wetted with asolvent to remove surface particles of decomposed material from saidlayer.

4. An apparatus for regenerating a photoconductive layer having asubstantial amount of an organic material which has been utilized in anelectrophotographic process comprising means for removing surfaceparticles of said photoconductive layer from the remainder of the layer,said means being mounted relative to the said layer for contacttherewith.

5. The apparatus of claim 4 wherein said photoconductive layer being onthe periphery of a'drum and said means for removing surface particles ofsaid layer being positioned adjacent said drum and contactable with thesurface of said layer opposite the surface thereof affixed to the saiddrum.

6. An electrophotographic duplicating process comprising fonning alatent electrostatic image on a photoconductive layer having asubstantial amount of an organic material, transferring the latentelectrostatic image on said layer to a receiving material andperiodically regenerating said photoconductive layer for reuse byremoving surface particles of said photoconductive layer from theremainder of said layer before forming a latent electrostatic image.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 13,910,697

DATED 1 October 7, 1975 INVENTOR(S) Willi Lanker It is certified thaterror appears in the aboveidentified patent and that said Letters Patentare hereby corrected as shown below:

IN THE SPECIFICATION:

Column 14, line 31, "test should read --text-- Column 16, line 13,"presence should read --pressure-- Column 17, line 28, "rotated at"should read --rotated at from-- Column 18, line 18, "or" should read--of- Signed and Sealed this eleventh Of May 1976 A A nest:

RUTH C. MASON C.-MARSHALL DANN Arresting ()j'fivvr ("ummixsimu'rnj'lau'nls and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION PATENT NO. 3, 910, 697

DATED I October 7, 1975 INVENTOR(S 1 Willi Lanker It is cerhfied thaterror appears in the aboveidentified patent and that said Letters Patentare hereby corrected as shown below:

IN THE SPECIFICATION:

Column 14, line 31, "test" should read --1;ext-- Column 16, line 13,"presence" should read --pressure-- Column 17, line 28, "rotated atshould read --rotated at frorn- Column 18, line 18, "or" should read--of-- Signed and Sealed this eleventh Day of May 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting ()jfir'r'r Commissioneruflau'nls and Trademarks

1. A process for regenerating a photoconductive layer having asubstantial amount of an organic material which has been utilized in anelectrophotographic process comprising removing surface particles of thephotoconductive layer from the remainder of the layer by applyingthermal radiation to the surface of said layer for removal of saidparticles of decomposed material by vaporization.
 2. A process forregenerating a photoconductive layer having a substantial amount of anorganic material which has been utilized in an electrophotographicprocess comprising removing surface particles of the photoconductivelayer from the remainder of the layer, wherein the removing includeswashing said layer with a solvent to remove surface particles ofdecomposed material from said layer.
 3. A process for regenerating aphotoconductive layer having a substantial amount of an organic materialwhich has been utilized in an electrophotographic process comprisingremoving surface particles of the photoconductive layer from theremainder of the layer, wherein said removing includes contacting saidlayer with a fibrous web wetted with a solvent to remove surfaceparticles of decomposed material from said layer.
 4. An apparatus forregenerating a photoconductive layer having a substantial amount of anorganic material which has been utilized in an electrophotographicprocess comprising means for removing surface particles of saidphotoconductive layer from the remainder of the layer, said means beingmounted relative to the said layer for contact therewith.
 5. TheapparatUs of claim 4 wherein said photoconductive layer being on theperiphery of a drum and said means for removing surface particles ofsaid layer being positioned adjacent said drum and contactable with thesurface of said layer opposite the surface thereof affixed to the saiddrum.